This invention relates to a liquid phenolic resole resin (hereinafter called liquid resole) for refractory uses, which is free from odor of formaldehyde during mixing with refractory materials, which has good storage properties in the form of a plastic mud or refractory mix, and which is free from irritating odor during processing of refractory articles which have improved dry strength.
Phenolic resins have been playing a major role in place of conventional coal tar and pitch in organic binders for refractory uses because they can be mixed under ambient temperature with aggregates, they have excellent dry strength, and they can improve the workshop environment during processing of refractories.
For refractory uses, phenolic resins such as novolac and resole resins are employed either jointly or alone in the form of liquid or powder. Some typical examples are powdered novolac resin containing hexamine (hexamethylene tetramine) that are employed with wetting agents such as ethylene glycol, glycerine, or denatured alcohol, or associated with liquid resole type resins.
On the other hand, resole type phenolic resins are employed as a solvent containing liquid resole resin, with a solvent such as ethylene glycol. Water soluble liquid phenolic resins are employed alone. Furthermore these liquid resins associated with powdered novolac type resins are employed.
However, there are drawbacks for each type of resin which must be overcome to meet the needs of certain industries. Novolac type phenolic resins, associated with hexamine and/or solvent such as ethylene glycol, make the work environment disagreeable by emitting a disagreeable odor during the processing of refractory materials. In the case of resole type phenolic resins, both water soluble and solvent containing liquid phenolic resins emit odor of formaldehyde during mixing of refractory materials.
Basic aggregates such as magnesia have recently increased in their demand. However, in the method of manufacturing refractory articles mainly containing such basic aggregates, problems are caused by employing the above-described water soluble or solvent containing liquid resins because the basic aggregates react with methylol groups of the resin structure, free water in said resins and the condensed water emitted in the drying stage of refractory articles. This often leads to the production of refractory articles that are particularly poor in durability, due to cracking during processing.
After much investigation to overcome the drawbacks that conventional novolac or resole type phenolic resins have on the performance of refractory articles, the present inventors have found the solution to the problem. The liquid resole according to the present invention is particularly effective for manufacturing refractory articles consisting of basic aggregates.